Deep brain stimulation (DBS) refers to the delivery of electrical pulses into one or several specific sites within the brain of a patient to treat various disorders. For example, DBS has been proposed as a clinical technique for treatment of chronic pain, essential tremor, Parkinson's disease (PD), dystonia, epilepsy, depression, obsessive-compulsive disorder, and other disorders.
A DBS procedure typically involves first obtaining preoperative images of the patient's brain (e.g., using computer tomography (CT) or magnetic resonance imaging (MRI)). The imaging process sometimes involves first affixing to the patient's skull fiducial markers that are discernable on the images produced by the imaging process. The fiducial markers assist in registering the preoperative images to the actual physical position of the patient in the operating room during the subsequent surgical procedure. Using the preoperative images, the neurosurgeon can select a target region within the brain, an entry point on the patient's skull, and a desired trajectory between the entry point and the target region. The entry point and trajectory are carefully selected to avoid intersecting or otherwise damaging critical brain structures.
In the operating room, the patient is immobilized and the patient's actual physical position is registered. The physician marks the entry point on the patient's skull and drills a burr hole at that location. A mechanism is provided to precisely control the path through the patient's brain to the desired location. Specifically, a positioning error on the order of a millimeter can have a significant negative effect on the efficacy of the DBS therapy. Stereotactic instrumentation and trajectory guide devices are commercially available products that facilitate the control of the trajectory and positioning of a lead during the surgical procedure.
A microdrive introducer can be used to insert a deep brain stimulation lead toward the selected region of the brain along the selected trajectory. The lead provides one or several conductive paths to deliver stimulation pulses to the selected region. The lead includes a very small diameter insulative lead body with one or several conductors (e.g., stranded wires) embedded in the insulative material. The lead also includes one or several electrodes at a distal end of the lead that are electrically coupled to respective conductors. The electrodes can be used to record signals within the brain and/or to deliver electrical stimulation pulses to brain tissue. Often, the electrical activity adjacent to one or several electrodes is analyzed to determine whether the recorded signals are consistent with the targeted region of the brain. If the recorded signals are not consistent with the targeted region, an adjustment to the lead's position can be made as appropriate.
A burr hole plug or cap structure is typically utilized to retain the lead in the desired position. A burr hole structure generally includes: (i) a ring or grommet-like element that is inserted into the hole first so as to protect the edges of the burr hole and (ii) a cap or plug device that is inserted into the ring or grommet-like element to secure the lead and plug the hole.
By way of example, in U.S. Pat. No. 6,044,304, a burr ring is disclosed that is secured to the skull. The burr hole plug of the '304 patent also has an upper flange portion and circumferential ribs used to position the plug in the cranium. Also, the burr hole plug described in the '304 patent includes an aperture capable of accepting a lead through a septum.
In U.S. Pat. No. 5,954,687, a device is disclosed for securing a catheter within a burr hole. The device has a series of spaced septum elements that can be selectively penetrated for fluid communication with a reservoir in the apparatus. The main objective of the device is to allow fluid access to the patient's brain through a burr hole. Anchoring of the device is not taught and there are a limited predetermined number of septum holes that can be accessed.
U.S. Pat. No. 5,927,277 describes a burr hole ring for retaining a probe relative to the skull. The burr hole ring has an engaging member with holes to receive a probe. The '277 patent also describes a method for securing a device at a desired orientation within the burr hole. Since a fixed spacing between holes is described, the device can be placed in a limited number of locations through the burr hole.
U.S. Pat. No. 5,865,842 discloses a system and method for anchoring a lead in a burr hole. The disclosed system consists of a base-plate, adaptor, seal, and screw cap. The lead is anchored mechanically at the burr hole at a 90 degree angle relative to the burr hole.
U.S. Pat. No. 5,843,150 discloses an annular clamping means with a compressible feed-through member for receiving a lead. The described order for anchoring the lead includes making the burr hole, inserting the plug ring, inserting the lead, and engaging the clamping member.
Other burr hole plug assemblies and features of burr hole plugs are taught in U.S. Pat. No. 5,464,446 (burr hole plug with a central lumen and a cap that engages with the flange of the plug); U.S. Pat. No. 4,998,938 (a device that facilitates insertion of an instrument into a patient's cranial cavity); U.S. Pat. No. 4,328,813 (a burr hole plug with a cap that anchors the lead); and U.S. Pat. No. 4,245,645 (a probe and system that is used to perform stereoelectroencephalographic exploration).